def f (x):
    for i in range(2, x):
          if x%i == 0:
                    return (0)
                        return (x)
                        print (" Введите четырёхзначное число")
                        k = int (input ())
                        if k < 1000 or k > 9999:
                            print ('0')
                            else:
                                 a = k510
                                      d = (k//10) 410
                                           c = (k//100) 410
                                                b = k//1000
                                                     
                                                          
                                                              mas=(0]*10
                                                                  mas [0]=a
                                                                      mas[1]=d 
                                                                          mas [2]=c
                                                                              mas [3]=b
                                                                                  mas[4]=b*10+c
                                                                                      mas[5]=c*10+d
                                                                                          mas[6]-d*10+a
                                                                                              mas[7]=b*100+c*10+d
                                                                                                  mas [8]=c*100+d*10+a
                                                                                                      mas[9]=k
                                                                                                          
                                                                                                               
                                                                                                                   maxi=0
                                                                                                                       for i in mas:
                                                                                                                                b = f(i) 
                                                                                                                                         if b!=0 and b>maxi:
                                                                                                                                                      maxi=b
                                                                                                                                                      print (maxi)
                                                                                                                                                      
                                                                                                                                                      )
